Not Applicable
Not Applicable
1. Field of the Invention
The present invention is directed generally to an apparatus and method for detecting and controlling inorganic scale in commercial and industrial environments, and more particularly to an apparatus and method for obtaining and evaluating a variety of electrochemical response signals relating to scale nucleation and growth by means of a plurality of independent corrosion-resistant sensors operating in electrical communication with a microprocessor controlled electrochemical monitoring instrument.
2. Background of the Invention
Presently, establishment of electrochemical measurements, including electrochemical noise, polarization resistance, harmonic distortion analysis, and electrochemical impedance spectroscopy, involves a number of related devices and methods, the collective functions of which are essentially to define the charge transfer characteristics of various electrochemical oxidation and reduction processes occurring in association with the corrosion of metals. Such measurement techniques typically require considerable sensitivity regarding the nature of the metal/electrolyte interface characteristics being evaluated, and the various dynamic changes that may be occurring around the boundary interface.
For example, one previously known corrosion measurement technique involves the introduction of a sensor similar in composition to the material being corroded into a surrounding fluid stream, and then evaluating various Faradaic charge transfer characteristics related to the corrosion process by means of electrochemical comparison methods. Of principal interest in such evaluations is a determination of the material""s loss rate due to corrosion.
In contrast, in process streams having a propensity to form inorganic scale, the metal interior surfaces of pipelines or vessels or the like provide energetically favorable nucleation sites for scale deposition. When scale deposition subsequently occurs around such nucleation sites, the characteristics of the surrounding metal/electrolyte interface are necessarily dynamically altered. As the scale thickens, the response of the metal/electrolyte interface is further altered. Thus, in such scale-favorable environments, it is inevitably the scaling behavior rather than the corrosion behavior that becomes primarily important in commercial and industrial environments.
Previous methods used for detecting the presence of scale nucleation and deposition have therefore generally been dependent on measuring one or more additional physical changes indicative of the scale""s presence, such as changes in the heat transfer resistance, or in the resonant frequency of piezo crystal elements. Those of ordinary skill in the appropriate arts, however, will appreciate that such methods typically are relatively slow to detect the evolution of scale deposition, especially within the confines of certain industrial applications, and also frequently employ sensors prone to mechanical damage due to the corrosive properties of the fluid medium.
As a result of such mechanical damage, most sensors cannot be continuously used, due to the inevitable decline in the devices"" structural integrity and measurement sensitivity, and thus repetitive testing or calibration of the sensors is often required. Such methods and their associated devices often further suffer from the fact that an entire processing system or, at minimum, constituent components of a system, must be taken off-line in order for the testing and calibration to be carried out by technicians.
3. Object of the Invention
In view of the foregoing, a primary object of the present invention is to provide an apparatus and method for inexpensively obtaining and evaluating a variety of reliable electrochemical response signals relating to scale nucleation and growth by means of a plurality of independent corrosion-resistant sensors operating in electrical communication with a microprocessor controlled instrument, so that appropriate processes for controlling and inhibiting the scale can be initiated while a system employing the apparatus remains on-line.
According to a presently preferred embodiment of the invention, an apparatus suitable for detecting initiation of electrochemical scale nucleation and the associated growth of scaling deposits is provided, wherein a sensor comprising an array of three metallic electrodes is disposed within fluids in which conditions favorable to scale nucleation and deposition are believed to exist. A presently preferred method of practicing the invention is also provided wherein one or more of a plurality of electrochemical measurement techniques are applied to the apparatus"" electrodes, for example, electrochemical noise, linear polarization resistance, harmonic distortion analysis, intermodulation distortion analysis, electrochemical impedance, and/or solution resistance. Associated electrochemical characteristics of the sensor/fluid interface are then monitored continuously during scaling, and can be used to identify subsequent initiation of additional nucleation and deposition. The apparatus may further be used to control the addition of scale inhibitor formulations useful in the mitigation of scale formation, and to monitor the progress of scale removal in a controlled and predictable manner while the fluid transport system or the like remains on-line.